Is a Landlord required to provide a mailbox in multifamily units?

[Shari Matousek]

I have a 4-plex located in the Denver, Colorado area.  The outside, free-standing group mailbox (it serves 3 other bldgs.) has been vandalized.  The Post Office claims they own it & are the only ones that can fix it.  They have declared it not repairable.  They are requesting that the Landlords supply them with a new box & pay for the cost of installation.  1) Does this sound right?, 2) Is a Landlord legally required to supply a mailbox for their Tenants use?  (All of the apartments are "legal" & each has it's own address.)  Many thanks for your feedback!